Vanadium(â…¤)adsorptiononto Goethite And Simulation Study On Its Speciation

An increasing seriousness of heavy metal contamination has caused a profound threat to human health.The surge of industrial activities has intensified more environmental problems as seen forexample in the deterioration of several ecosystems due to the accumulation of dangerous pollutants,such as heavy metals. Heavy metals are still being used in various industries due to their technological importance. Yet, untreated or imperfect treatment of waste products fromthese industries will carry other serious issues to human health and environment. Aside fromthe environmental damage, human health is likely to be affected as the presence of heavymetals beyond a certain limit brings serious hazards to living organisms. For instance, Vanadium is a trace element, which may be beneficial and possibly essential in biology but certainly harmful for humans and some living organisms if excessive.Therefore, heavy metal pollution treatment has become a widespread concern.Iron based materials, including iron hydroxides and zero-valent iron are usedsuccessfully for remediation of a variety of environmental pollutants. Goethite is always considered to be an important environmental material which can be functioned asadsorbents for heavy metals. It widely exists in soil particles and rock, aquatic sediment. Due to large specific surface area and more active sites, the nanoscale goethite is an excellent adsorption material and can affect the migration, distribution and transformation of many harmful heavy metals by adsorption.Vanadium pollution in Panzhihua area is a special environmental problem of China.Little work has been done on finding economical vanadium remediation techniques. The essay is based on the international cooperation project “Joint research on the key technology of the vanadium pollutiontreatmentin Panzhihua vanadium-titanium magnetite mine”supported by SCST. With the theme of experimental and simulation of vanadium adsorption on goethite,the goethitehas been prepared to research the adsorption of heavy metal element,vanadium. Some key factors have been revealed through SEM,EDS,XRD,etc. In addition, this article has researched the mechanism of adsorption of vanadium on goethite by the comparison experiments between adsorption testing and computer simulation.The main details and resultswere presented:1. The adsorption of vanadium onto the surface of goethite and many other heavy metals in different adsorption medium is similar, showing the trend of rapid adsorption.The initial process is almost instantaneous followed by a very slow process, and the adsorption capacity of vanadium will not undergoing significant changes.2. p H is an important factor among the influences of the adsorption of vanadium onto the surface of goethite. The lower p H contributes to the adsorption of vanadium on goethite, while the adsorption rate decreased with the increase of p H. This is the expected result, since the charge in goethite and vanadate ion surface become more and more negative. For the low concentration of vanadium solution, at about p H=4, both the adsorption capacity and removal rate reached the highest, what’s more, the removal rate reached almost one hundred percent. With the increase of p H, the removal rate gradually decreased, and then tended to be stable in the range of p H from 8 to 10 andfinallydropped rapidly. As for vanadium solution with high concentration, in the p H range throughout the study, the adsorption rate and adsorption capacity has not changed much.3.Effect of different dose of adsorbent on adsorption of high initial concentration of vanadium solution is obvious.The adsorbent 2.0g/Lof total vanadium concentration in the initial scope of the experimental design can provide sufficient adsorption capacity. In the designed concentration range of experiment, the ionic strength of solution hasn’t influenced the absorption of vanadium on goethite.4. By fitting the experimental data of adsorption isotherm at 15℃, 25℃, 35℃and under 4, 6, 8 p H conditions using Freundlich and Langmuir isotherm model, it was found that the Freundlich model of adsorption on goethite at all temperature and p H of vanadium adsorption data get the best fitting with correlation coefficient above 0.998.5. Through the experimental study on desorption of vanadium using EDTA-Na2, the desorption rate was small, but with the increase of goethite vanadium adsorption capacity has increased, and showing increased slowly increasing trend at first and then quick trend. It showed that the relative competitive adsorption ability of four kinds of ionsfollowed the sequence of PO3-4>SO2-4Cd2+>Pb2+after the study about the competitive adsorption on Pb2+, Cd2+,SO2-4and PO3-4coexisting in the solution.6. Using modified Tessier two-step sequential extraction for goethite at three initial vanadium concentrations, the result is that most of the vanadium is leached from the HCl extraction step indicating strong sorption mechanism.Finally, the thesis has studied the forms of vanadium on goethite after adsorption by PHREEQC. Itisdiscovered that the main form of vanadium in solution is H2VO-4 followed by HVO2-4and H3V2O-7.There are different adsorption mechanism of vanadium onto goethite surface in various p H, in low p H,the surfaces of goethite mainly combine with VO+ 2 to form Goe_s2O2V(OH)+ 2,but in high p H,they tend to combine with HVO2-4to form Goe_s2O2VO(OH).